1. Field of the Invention
The present invention relates to a plasma display panel for use in a display device or the like, and in particular relates to a plasma display panel that offers excellent color balance.
2. Related Art
Among various types of color display devices used for displaying images on computers, televisions, and the like, a plasma display panel (hereinafter, xe2x80x9cPDPxe2x80x9d) has become a focus of attention as a color display device that can realize a slim, lightweight, large-screen display device.
FIG. 1 is a partial perspective and sectional view of a conventional, typical PDP.
In this PDP, a front glass substrate 11 and a back glass substrate 12 are placed in opposition to each other, with barrier ribs 19 being interposed in between. On the surface of the front glass substrate 11 facing the back glass substrate 12, a plurality of display electrodes 13 and a plurality of display scan electrodes 14 (only two pairs of them are shown in the drawing) having a stripe shape are alternately aligned in parallel to each other. The plurality of display electrodes 13 and the plurality of display scan electrodes 14 are then coated with a dielectric layer 15 made of lead glass or the like, and further coated with an MgO protective film 16. This forms a front panel.
On the surface of the back glass substrate 12 facing the front glass substrate 11, a plurality of address electrodes 17 (only four of them are shown in the drawing) having a stripe shape are aligned in parallel, and a dielectric layer 18 made of lead glass or the like is formed on the back glass substrate 12 so as to cover the plurality of address electrodes 17. The barrier ribs 19 are formed between neighboring address electrodes 17. Lastly, back phosphor layers 20R, 20G, and 20B in each of the three colors red (R), green (G), and blue (B) are applied to the gaps between neighboring barrier ribs 19 on the dielectric layer 18. This forms a back panel.
The areas within discharge spaces 21 between the front glass substrate 11 and the back glass substrate 12 where the plurality of pairs of electrodes 13 and 14 intersect with the plurality of address electrodes 17 are cells for light emission. The discharge spaces 21 are filled with an inert gas that contains neon as a main component and a trace quantity of xenon as a buffer gas.
To produce an image display on this PDP, sustain discharge is induced between pairs of electrodes 13 and 14 in cells which should be illuminated, to emit ultraviolet light. This ultraviolet light excites the phosphor layers 20R, 20G, and 20B, as a result of which visible light of the three primary colors red, green, and blue is generated and subjected to an additive process. Hence a full-color display is produced.
The back phosphor layers 20R, 20G, and 20B used in such a PDP are constructed so that favorable color balance is preserved when displaying a white color. Here, the luminance (light intensity) of each of the back phosphor layers 20R, 20G, and 20B in their initial states is different due to different compositions of the red, green, and blue phosphors. To maintain the color balance of the PDP in its initial state and thereby keep the color temperature from decreasing, such a technique has been employed as to set the back phosphor layer 20B having low luminance wider than the back phosphor layers 20R and 20G, or to reduce sustain discharge pulses for the back phosphor layers 20R and 20G through signal processing by a PDP drive circuit, in order to balance the luminance of red and green light with the luminance of the blue light.
Nevertheless, the PDP has the following problems associated with color temperatures.
First, the back phosphor layers 20R, 20G, and 20B deteriorate with illumination time of the PDP, due to the factors such as ion bombardment and ultraviolet radiation during discharge. This means the luminance of each back phosphor layer degrades over time. Here, since the deterioration speeds of the three back phosphor layers differ due to their different compositions, the deteriorating luminance of each back phosphor layer varies by greater amounts as time passes. This disturbs the color balance of the PDP when displaying a white color, and results in a drop in color temperature. Although the color balance can be adjusted to some extent through signal processing by the PDP drive circuit, it is more desirable to keep the color balance as constant as possible.
Second, the aforementioned signal processing technique has conventionally been employed to limit the use of the luminance of the red and green phosphor layers to balance the red light luminance and the green light luminance with the lower blue light luminance, in order to raise the color temperature of the PDP in its initial state. However, such limited use of the luminance of the red and green phosphors causes a decrease in brightness of the PDP.
The first object of the present invention is to provide a PDP that can maintain favorable color balance for a long time.
The second object of the invention is to provide a PDP with improved brightness in its initial state.
The first object can be fulfilled by providing front phosphor layers respectively in opposition to back phosphor layers, other than a back phosphor layer whose luminance degrades fastest with time, among red, green, and blue back phosphor layers. Since the front phosphor layers are susceptible to luminance deterioration due to ultraviolet radiation and ion bombardment, they serve to accelerate the luminance degradation speeds of the opposite back phosphor layers. Accordingly, the luminance degradation speeds of the back phosphor layers combined with the front phosphor layers are brought to be more balanced with the luminance degradation speed of the back phosphor layer whose luminance degrades fastest, with it being possible to maintain the color balance of the PDP for a long time.
The second object can be fulfilled by providing front phosphor layers respectively in opposition to back phosphor layers, other than a back phosphor layer whose initial luminance utilization factor is the lowest among the red, green, and blue back phosphor layers. In so doing, the back phosphor layers combined with the front phosphor layers increase in luminance, so that the brightness of the PDP in its initial state can be improved while maintaining favorable color balance.
High brightness and favorable color balance of the PDP can also be attained by providing front phosphor layers respectively in opposition to the red, green, and blue back phosphor layers, and setting the visible light transmittance of each front phosphor layer in accordance with the initial luminance of its opposite back phosphor layer.
Here, by using spherical phosphor particles obtained by hydrothermal synthesis for such front and back phosphor layers, the brightness of the PDP is further enhanced.